The subject matter described herein generally relates to semiconductors. In one embodiment, techniques described herein provide composition and film thickness information on production semiconductor wafers.
Due to the decreasing size of semiconductor device dimensions, film stack structures have become more complicated to produce and are frequently composed of newer materials. Thus, it has become important to monitor both film thickness and composition during production.
Auger Electron Spectroscopy (AES) and Electron Probe Micro Analysis (EPMA) have been used for film thickness and composition measurement. AES is generally a surface sensitive technique and is usually used for ultra-thin film analysis. Because of the short mean free path of Auger electrons, AES may not be a practical technique for analysis of films thicker than 100 Å. In addition, Auger electron emission probability decreases with atomic number (FIG. 1). Hence, AES has a reduced signal-to-noise ratio (S/N) for heavy element composition analysis.
Furthermore, since X-rays may escape from larger depths in solids than Auger electrons, EPMA may be used to measure films up to about 1 μm thick. However, EPMA may have poor S/N for light elements, such as Boron, Nitrogen, Oxygen, Carbon, Fluorine, and Phosphorus, because of the low X-ray fluorescent yield for light elements (FIG. 1). A long acquisition time may be needed to obtain reasonable precision for light element measurements, which is not preferable for in-line production monitoring. In many cases, it may be difficult for EPMA to be used to determine film composition, if the film layer being tested contains the same element as other layers within the stack. Although double or multiple landing energy methods may help to solve this problem, these methods may suffer from other disadvantages, such as slow measurements, instability of electron beam, and difficulty in accurate control of electron and solid interaction volume.